1. Field of the Invention
The present invention relates to an image forming device having an electrophotographic printing device of a facsimile machine, a copy machine or a printer (including a Multi Functional Peripheral (MFP) of these machines) or the like. In particular, the present invention relates to a structure for relatively positioning an optical writing head, which writes optical image information on a uniformly charged surface of a photoconductive drum and forms an electrostatic latent image, with respect to the photoconductive drum.
2. Description of Related Art
In the electrophotographic printing device, a photoconductive drum is embedded in a drum unit (a drum cartridge) or a process unit (a process cartridge) which also includes a developing unit. The photoconductive drum is positioned in a main frame of an image forming device via these units. With respect to these units, an optical writing head (a light emitting element array) is positioned at a proper relative positional relationship with the photoconductive drum.
FIG. 6 shows an example of a conventional image forming device. A photoconductive drum 110 is supported rotatably on its axis in a unit housing 101. A photoconductive drum unit 100 including the unit housing 101 is provided at a prescribed position of a main frame of the image forming device. In the example shown in FIG. 6, an optical writing head 120 formed of a Light Emitting Diode (LED) is attached inside a maintenance cover 130 of the image forming device. When the cover 130 is closed, the photoconductive drum 110 and the optical writing head 120 are positioned relatively to one another. In the conventional example, a concave part 102 is formed on a surface of the housing 101. A positioning pin 121 is provided on the optical writing head 120. When the cover 130 is closed, the positioning pin 121 is received in the concave part 102. As a result, the optical writing head 120 is positioned to be located at a proper relative position with respect to the photoconductive drum 110.
In the example shown in FIG. 6, the photoconductive drum unit 100 includes the housing 101 formed of synthetic resins, a drum shaft 111 fixed on the housing 101 and the photoconductive drum 110 supported rotatably on the drum shaft 111. Furthermore, the photoconductive drum unit 100 includes a charger 103 and a toner cleaner 104 and is unitized. The photoconductive drum unit 100 is positioned at a prescribed position of the image forming device (not shown) by the drum shaft 111. When the cover 130 is closed, the positioning pin 121 is received in the concave part 102 formed on the surface of the housing 101. Consequently, the optical writing head 120 is positioned.
A positional relationship between the optical writing head 120 and the photoconductive drum 110 is influenced by the accuracy of the relative position of the photoconductive drum 110 and the drum shaft 111 and the accuracy of the relative position of the drum shaft 111 and the housing 101. Therefore, there are cases in which the accuracy of the positioning decreases. In particular, since the housing 101 is formed of synthetic resins, the measurement of the housing 101 is prone to be uneven. This fact is a great factor for decreasing the accuracy of the relative position of the optical writing head 120 and the photoconductive drum 110.
The above positioning is not based on a relative position with respect to the printing paper which is printed while being transported. Therefore, when a toner image on the surface of the photoconductive drum is transferred onto the paper, there are cases in which a prescribed transfer position on the paper is displaced. Furthermore, it is necessary to separately attach the positioning pin on a commercially available LED array. As a result, there is a drawback that a number of components and a number of assembling steps increase.
Therefore, there is a demand for an image forming device which can improve the accuracy of the relative position of the optical writing head and the photoconductive drum or which can reduce the number of components.